有色金属(冶炼部分)

以废旧磷酸铁锂为研究对象，采用硫酸钠辅助氧化焙烧—水浸工艺选择性优先回收金属Li。从热力学角度系统分析了Li、Fe、P在不同温度下的赋存形态及其稳定性规律，考察了焙烧过程中焙烧温度、物料摩尔比、焙烧时间以及水浸过程中液固质量比、反应温度和时间等因素对Li、Fe、P浸出率的影响。结果表明，硫酸钠辅助氧化焙烧最佳条件为：焙烧温度700℃、废旧磷酸铁锂和Na_2SO₄物料摩尔比1.5、焙烧时间3 h；水浸最佳条件为：反应温度60℃、液固质量比4、时间1 h。在上述最佳条件下，Li、Fe、P浸出率分别为96.58%、0.09%、0.18%。X射线衍射及扫描电镜-能谱结果表明，在700℃的焙烧温度下，LiFePO₄中的Li⁺与SO₄²-生成Li_2SO₄通过水浸进入水浸液，Fe和P分别以Fe_2O₃和Na_3Fe₂(PO₄)₃混合物的形式留在水浸渣中。

Amid the global low-carbon transition, lithium iron phosphate(LFP) batteries have established themselves as a pivotal technology for new energy vehicles and grid-scale energy storage applications, owing to their demonstrated safety advantages and economic viability. With the exponential growth in installed capacity worldwide, the impending large-scale decommissioning of these power sources has created an urgent need for efficient recycling methodologies to ensure sustainable lithium resource management and mitigate potential environmental impacts. The established recycling technologies, such as hydrometallurgical method, pyrometallurgical method, physical restoration, and direct regeneration, each present significant limitation that hinder it widespread adoption. Hydrometallurgical processes consistently achieve high leaching efficiencies but are plagued by substantial chemical consumption, wastewater treatment challenges, and associated environmental concerns. Pyrometallurgical approaches demonstrate robust capacity for processing large volumes of spent batteries but exhibit characteristically low lithium recovery rates and generate substantial carbon emissions due to their high-temperature operations. Physical restoration techniques offer a cost-effective alternative but remain constrained by their sensitivity to variations in the consistency and composition of feed materials. Direct regeneration methods successfully restore the electrochemical performance of cathode materials but demand extremely uniform precursor materials and require considerable capital investment in specialized equipment. To address these challenges, particularly the critical issue of lithium-iron separation in spent LFP cathodes, an innovative recycling methodology was developed based on sodium sulfate-assisted oxidative roasting followed by water leaching for preferential lithium extraction. Through systematic parameter optimization, the ideal conditions were determined as roasting at 700 ℃ for three hours with molar ratio of LFP to Na₂ SO₄ of 1.5, followed by water leaching at 60 ℃ for one hour with liquid-to-solid mass ratio of 4. Under these optimal conditions, the process achieves a remarkable lithium leaching efficiency of 96.58%, while simultaneously suppressing the co-dissolution of iron and phosphorus to exceptionally low levels of 0.09% and 0.18%, respectively. This represents a significant advancement in selective lithium recovery technology, effectively achieving deep separation of lithium from iron-phosphorus impurities and resolving the long-standing challenge of elemental co-leaching that has persistently troubled conventional hydrometallurgical processes. The underlying reaction mechanisms and phase transformation pathways were systematically investigated using multiscale characterization techniques, revealing a complex sequence of structural changes during thermal treatment. The transformation process exhibits distinct stage-wise characteristics: at 400 ℃, Fe~2+ oxidation to Fe_2O₃ occurred alongside initial degradation of the LiFePO₄ crystal structure; at 500 ℃, the original olivine structure underwent complete disintegration, facilitating Li⁺ release and enabling the formation of Na₃ Fe₂(PO₄)₃; at 600 ℃, lithium ions combined with sulfate anions to generate water-soluble Li₂ SO₄; within the range of 700–800 ℃, the melting of Na₂ SO₄ created localized oxygen-deficient environments that inhibited complete Fe~3+ oxidation, as visually evidenced by the material's color transition from bright red to dark purple and further confirmed through SEM-EDS analysis. During the subsequent water leaching stage, Li₂ SO₄ and any unreacted Na₂ SO₄ are selectively extracted into the aqueous phase, while the iron-phosphorus compounds remain exclusively in the solid residue. Comprehensive characterization of the leached residue confirms the presence of only Na₃ Fe₂(PO₄)₃ and Fe_2O₃ phases, with sulfur elemental signals becoming virtually undetectable, thereby providing compelling experimental evidence for the successful and nearly complete separation of lithium from the iron-phosphorus matrix. This research has successfully delineated the comprehensive stepwise mechanism encompassing structural decomposition-lithium release–sulfationselective leaching, establishing a technically robust and industrially viable pathway for the value-added recycling of spent LFP batteries while providing crucial theoretical foundations for the selective recovery of valuable elements from complex multi-component material systems in sustainable resource management.